A comparison of design decisions made early and late in development

DS 87-2 Proceedings of the 21st International Conference on Engineering Design (ICED 17) Vol 2: Design Processes, Design Organisation and Management, Vancouver, Canada, 21-25.08.2017

Year: 2017
Editor: Anja Maier, Stanko Škec, Harrison Kim, Michael Kokkolaras, Josef Oehmen, Georges Fadel, Filippo Salustri, Mike Van der Loos
Author: Tan, James; Otto, Kevin; Wood, Kristin
Series: ICED
Institution: 1: Singapore University of Technology and Design, Singapore; 2: Aalto University, Finland
Section: Design Processes, Design Organisation and Management
Page(s): 041-050
ISBN: 978-1-904670-90-2
ISSN: 2220-4342


The occurrence rates and cost impact of design changes made early and later in the design process were studied, to test and quantify the 80-20 rule of design cost impacts, that early design decisions account for the majority of costs in a development program. Cost and schedule impact of decisions made throughout the development process was carried out at a large aerospace firm on two programs covering 7 years of development with 275 person-years effort. The underlying data used was the rate and cost of design changes made. We found no significant difference in the rate of occurrence of design change decisions made, but we found a significant difference in the cost impact of the design changes. Overall, early design change decisions cost 5 times more than later design change decisions. This difference is primarily due to the inability to determine if an early design decision is correct until later in development during testing.

Keywords: Requirements, Project management, Process modelling, Early design phases


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